Method for selecting the operating state of a cruise control system for motor vehicles

ABSTRACT

A method for selecting the operating state of a cruise control system for motor vehicles having a distance sensor and automatic blindness detection, in which at least one additional condition is checked for automatic shutdown of the cruise control when blindness of the distance sensor is detected, and a shutdown is performed only when this additional condition is also met.

RELATED APPLICATION INFORMATION

This application claims the benefit and priority of PCT/DE02/0373, whichwas filed on Sep. 30, 2002 and which designated the United States ofAmerica, and claims priority to and the benefit of German PatentApplication No. 102 11 475.7, which was filed in Germany on Mar. 15,2002 (both of which are incorporated in their entirety as to theirdisclosures).

FIELD OF THE INVENTION

The present invention relates to a method for selecting the operatingstate of a cruise control system for motor vehicles having a distancesensor and automatic blindness detection, and it also relates to acruise control system for implementing this method.

BACKGROUND INFORMATION

There are cruise control systems with which the speed of the vehicle maybe regulated at a desired speed selected by the driver for vehicles. Inaddition, the distance from a vehicle in front is measurable with thehelp of a distance sensor, e.g., a radar or lidar sensor. The cruisecontrol is then adjusted to maintain a predetermined distance, which maybe as a function of speed, from the vehicle traveling in front, whichhas been selected as the target object. Such systems are also referredto as adaptive cruise control or ACC systems.

Satisfactory functioning of an ACC system presupposes that the distancesensor is functioning faultlessly and is correctly adjusted so thatvehicles traveling in front in one's own lane may be located reliably.Apart from a disturbance in function or a misadjustment of the distancesensor, environmental factors such as heavy rain or snowfall, soiling ofthe sensor head or the like may result in a reduction in sensor rangeeven to the extent of the distance sensor becoming blind. In general,the function of radar sensors is less impaired than that of lidarsensors by rain or snowfall, but even with radar sensors there is therisk of the sensor being blinded in particular when the radar antennamounted in an exposed position on the front of the vehicle becomesencrusted with snow, ice or sludge thrown up from the road. For safetyreasons, it is desirable for the blindness of a distance sensor to bedetected automatically and then for a shutdown of the ACC system to betriggered and an acoustic or visual warning to be output to the driver.

German patent document no. 196 44 164 A1 refers to and discusses anautomotive radar system in which a dielectric body which is used forfocusing the radar waves is covered with printed electric conductorswhich allow detection of a layer of dirt, snow or moisture thatinterfere with radar reception. If necessary, the interfering depositmay also be removed automatically, e.g., by electric heating or by atype of wiper. However, such monitoring and cleaning systems arerelatively complex and expensive.

German patent document no. 199 45 268 discusses and refers to a methodwhich provides for recognizing blindness of a radar sensor merely on thebasis of the signals supplied by the radar sensor itself. By analyzingthese signals, various indicators are formed which indicate blindness ofthe sensor with a relatively high reliability, depending on the drivingsituation. Examples of suitable indicators include the angle quality ofall objects detected by the radar system, this quality describing theobject's stability, i.e., the rate of detection failures of the targetobject selected for the regulation, the average power of the signalsreceived by the sensor, the sum of all objects detected by the systemduring a measurement, the relationship between the object distance andthe radar amplitude for the object detected at the greatest distancefrom one's own vehicle and the presence or absence of road reflection.These indicators are weighted with weighting factors which may in turnbe variable, depending on the traffic situation, and a decision signalindicating whether or not the sensor is blind is obtained by comparingthe resulting weighted sum of the indicators with a threshold value.

With regard to the traffic situation, a distinction between followingand driving freely is relevant for detection of blindness. Followingrefers to a traffic situation in which a vehicle traveling directly infront is selected as a target object and is followed at an appropriateddistance. In this situation, a sudden loss of the target object is animportant indicator of blindness. Driving freely refers to a trafficsituation in which no relevant target object is selected but instead thecruise control relies on the desired speed selected by the driver.However, even in this situation, the sensor will in general also detectother radar targets, e.g., street reflection, movable targets orstationary targets at the edge of the road, vehicles in other lanes andthe like. The radar echoes of these targets may then be used fordetection of blindness.

When blindness of a sensor is detected with such a system, whetherdriving freely or following, this results directly in shutdown of theACC system and the driver is prompted by a takeover instruction to takecontrol of the longitudinal movement of the vehicle himself using theaccelerator pedal and brake.

SUMMARY OF THE INVENTION

An object of the exemplary embodiment and/or exemplary method of thepresent invention is to improve the automatic selection of the operatingstate of the cruise control system, in particular the choice betweenactive and inactive states of the ACC system, so that a highavailability of the ACC system and a system response that is plausiblefor the driver are achieved in a wide range of operating situationswhile appropriately taking into account the results of the blindnessrecognition.

This object maybe achieved according to the exemplary embodiment and/orexemplary method of the present invention with a method in which atleast one additional condition is checked for the automatic shutdown ofthe cruise control system when a distance sensor is found to be blindand a shutdown is performed only when this additional condition is met.

The exemplary embodiment and/or exemplary method of the presentinvention is based on the consideration that automatic blindnessdetection has only a limited reliability in certain operating systems,thus potentially resulting in unjustified shutdown of the ACC system,which might seem implausible for the driver and could have a negativeeffect on the convenience and sense of safety of the driver. Forexample, when driving freely in a sparsely populated region such as adesert, it may occur that due to the lack of reflecting radar targets,blindness of the radar sensor is simulated, so that an unjustifiedshutdown of the ACC system is triggered. The driver must then intervenein the driving process himself apparently without a recognizable reason;this is often perceived as an inconvenience and also causes a loss ofconfidence in the reliability of the ACC system.

Therefore, according to the exemplary embodiment and/or exemplary methodof the present invention, when blindness of the distance sensor (eitherreal or presumed) is detected, a check is performed to determine whetherthere is at least one additional condition which would make shutdown ofthe ACC system appear plausible and necessary. Such a condition willprevail in particular when the vehicle is following another vehicle atthe time when the blindness is detected. In this situation there is ahigh probability that the detection of blindness is an indicator of trueblindness of the distance sensor, and moreover it is appropriate in thissituation for safety reasons to point out to the driver as a preventivemeasure the possibility of a malfunction in the ACC system. In freedriving, however, there is a much higher probability that blindness ofthe sensor is only being simulated because of the absence of suitablereflective targets, and even if there is a true case of blindness, thereis no immediate risk if the cruise control is continued at the desiredspeed.

However, in the context of the exemplary embodiment and/or exemplarymethod of the present invention, conditions may also be tested whichmake a shutdown of the ACC function appear appropriate even when drivingfreely. For example, in a case when blindness of the distance sensor isdetected when driving freely, it would be conceivable to check whetherthe car was following another vehicle within a certain period of time inthe past or whether it has passed a vehicle previously traveling infront. This would indicate that there is relative activity on the roadon which the vehicle travels, so that reappearance of a vehicletraveling in front in one's own lane would be expected and the drivershould be informed of the presumed blindness of the distance sensor as aprecautionary measure.

With a radar sensor, soiling of the sensor due to snow, sludge or ice isthe most common cause of blindness, so a supplementary check could alsobe performed on the basis of whether or not the windshield wiper hasbeen turned on, on the basis of an outside temperature sensor, or on thebasis of traction control or wheel slip to ascertain whether trueblindness of the radar sensor due to ice, snow or sludge or possiblyeven rain is plausible.

Advantageous embodiments of the exemplary embodiment and/or exemplarymethod of the present invention are described herein.

In one embodiment of the present invention, the only condition checkedis whether the vehicle is following another vehicle. When drivingfreely, however, ACC cruise control will be continued even in the eventblindness is detected. According to another embodiment of the presentinvention, however, the driver may be warned that the sensor might beblind by an acoustic and/or visual signal when blindness is detectedwhen driving freely. If no such warning is provided, then of course noblindness check need be performed in the first place when drivingfreely.

If the ACC function has been turned off when following or because ofother conditions, this usually results in deceleration of the vehiclewhich is definitely perceptible for the driver and on the basis of whichthe driver is able to recognize that the ACC has been shut down.However, it is expedient to additionally inform the driver of theshutdown by a signal (takeover instruction). If a target object isrecognized after such a shutdown, the ACC may automatically resumecontrol, because then the blinding of the distance sensor will haveevidently been eliminated or there was no true blinding. In analternative embodiment, however, the system may be designed in such away that the ACC may only be reactivated by a driver command.

In a modified embodiment, the cruise control function may be continuedat the desired speed when blindness is detected when driving freely, inwhich case distance monitoring is inactivated and the driver is informedof this circumstance by a signal. Again in this case, distancemonitoring may be reactivated automatically on detection of a new targetobject or only in response to an explicit driver command.

According to another embodiment of the present invention, instead of thecondition “following,” a check is performed to determine whether theblindness currently detected is the first detection of blindness sincebeginning the trip or within a certain period of time. An initialblindness detection will then result in shutdown of the ACC systemeither when following or when driving freely. If the driver recognizesthat he is in an environment having very little reflection and blindnessdetection is therefore likely to be wrong, the driver will reactivatethe ACC through a corresponding command. If the blindness detectionsystem then again displays the blinding of the sensor, the higher levelcontrol system will have “learned” that the automatic shutdown does notconform to the driver's wishes and the ACC function will be maintainedfor at least a limited period of time. The length of this period of timemay be variable and will be selected to be longer, the more frequentlythe driver has reactivated the system. As an alternative, the driver maybe given an opportunity to directly input a command “ignore blindnessdetection” which will then remain in effect until the end of the trip oruntil canceled by the driver. The additional condition to be checked inthis case is that the “ignore blindness detection” command is notactive. For safety reasons, there should be an initialization at thebeginning of the trip, i.e., when turning on the ignition, which makesthe “ignore blindness detection” command inactive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of significant components of an ACCsystem in a motor vehicle.

FIG. 2 shows a flow chart for an exemplary method of the presentinvention.

FIG. 3 shows a flow chart for another exemplary method of the presentinvention.

FIG. 4 shows a flow chart for another exemplary method of the presentinvention.

FIG. 5 shows a flow chart for another exemplary method of the presentinvention.

DETAILED DESCRIPTION

Motor vehicle 10 shown in FIG. 1 has a radar sensor mounted as adistance sensor 12 on the front section of the motor vehicle, with anACC control unit 14 also being mounted in the sensor housing. ACCcontrol unit 14 is connected by a databus 16 (CAN) to an electronicdrive control unit 18, a transmission control unit 20, a brake systemcontrol unit 22, and control unit 24 of a man/machine interface (MMI).

With the help of a multi-beam radar, distance sensor 12 measures thedistances, relative speeds and azimuth angles of objects which reflectradar waves and are situated in front of the vehicle. The raw datareceived at regular intervals, e.g., every 10 ms, is analyzed in ACCcontrol unit 14 to identify and track individual objects and torecognize in particular a vehicle traveling in the same lane in front ofone's own vehicle and to select it as a target object. Through commandsto drive control unit 18 and brake system control unit 22, as well ascommands to transmission control unit 20 in the case of vehicles havingan automatic transmission, ACC control unit 14 regulates the speed ofvehicle 10. The man/machine interface which is controlled by controlunit 24 includes various operating and display elements on the dashboardof the vehicle and is used among other things to transmit operatingcommands from the driver to ACC control unit 14 and to output messagesof an ACC control unit 14 to the driver. To this end, the MMI may alsohave a loudspeaker output for acoustic signals or for synthetic speech.

If no vehicle traveling in front is located, ACC control unit 14regulates the speed of vehicle 10 at a desired speed selected by thedriver. However, if a vehicle traveling in front is detected as a targetobject and its speed is lower than that of one's own vehicle, the speedof vehicle 10 is regulated to maintain an appropriate distance from thevehicle traveling in front.

The design and operation of such an ACC system are discussed, forexample, in Winner: “Adaptive Cruise Control” in Automotive ElectronicsHandbook, Ronald K. Jurgen (ed.), 2^(nd) edition, McGraw-Hill (1999),chapter 30.1.

As understood from the related art, ACC control unit 14 includesself-test functions which permit a function test of the distance sensorand its analysis system with the help of suitable test signals in aninitialization phase at the start of a trip. Likewise, this control unitincludes test functions which permit a continuous or periodic blindnesscheck of distance sensor 12 while driving, e.g., by analyzing thereceived radar signals referred to and discussed in German patentdocument no. 199 45 268.

FIG. 2 shows a flow chart of a method which is also implemented indistance sensor control unit 14 and which determines how blindnessdetection is to be performed when driving while an ACC system is activeand how this will effect the operating state of the ACC system.

After system start in step S1, immediately after turning on the ignitionof the vehicle, a detection check is first performed in step S2,checking on the functional capability of distance sensor 12 according toavailable methods. The positive or negative outcome of this detectioncheck is stored. If the result of the detection check is negative, anerror signal may optionally be output immediately via control unit 24and the man/machine interface. However, this is not obligatory becausethe vehicle is capable of being driven even without a functioning ACCsystem.

A check is then performed periodically in step S3 to determine whetherthe ACC system has been activated by a driver command. If the driver hasinput an activation command, the stored result of the detection checkperformed in step S2 is queried in step S4. If an error is found in thedetection check, an error signal is again output in step S5, informingthe driver that the ACC system is not usable. Otherwise, the ACC systemis activated in step S6.

When the ACC system is active, signals of distance sensor 12 areanalyzed, and a decision is made as to whether there is another vehicledirectly in front of vehicle 10 traveling in the same lane, which isthen selected as the target object. If there is such a target object,the system is in “following” mode and the distance from the vehicle infront is regulated. If no relevant target object is detected, then thesystem is in “free driving” mode and the speed of the vehicle isregulated at the desired speed selected by the driver.

A check is performed in step S7 to determine whether the mode is“following.” If this is not the case, the system remains in free drivingmode and step S7 is repeated cyclically.

Only if the system is in following mode is a blindness check of distancesensor 12 performed in step S8, e.g., on the basis of the absence or thequality of a radar echo signal from the selected target object andtaking into account any radar echoes from other radar targets. If theblindness check reveals that the distance sensor has not been blinded,the routine jumps back to step S7, and steps S7 and S8 are repeatedcyclically as long as the system remains in following mode. Depending onthe traffic situation, one or more changes between following mode andfree driving mode may occur. The blindness check is performed only infollowing mode each time.

If the blindness of distance sensor 12 has been recognized in step S8,then in step S9 the ACC system is deactivated and the driver receives atakeover instruction via control unit 24 and the MMI, instructing thedriver that he must take over control of the vehicle himself because theACC system has been turned off because of presumed blindness of thedistance sensor. The routine then jumps back to step S3. If the driverhas the sense that the blindness of the distance sensor has beenovercome—e.g., because of a change in weather conditions—the driver maythus reactivate the ACC system at any time.

Since step S8 is run through only in following mode, the cruise controlremains active in any case in free driving mode, so the driver is notburdened unnecessarily by the takeover instruction.

If, after a successful system shutdown in step S9, the driverreactivates the ACC system in step S3, the cruise control function willbe usable again in general even if the blindness of distance sensor 12still persists. If the sensor is blinded, it may not be possible todetect and select a relevant target object, so the query in step S7 asto whether the following mode is prevailing will have a negative outcomeand therefore a blindness check will not be performed again. Of coursein this case, the driver himself must watch for vehicles traveling infront.

The embodiment described here has the advantage that there is no falsedetection of blindness and thus no unnecessary shutdown of the ACCsystem in free driving in a low-reflection environment, where blindnessof the distance sensor would otherwise be simulated. This isadvantageous in particular for users of vehicles who frequently maketrips on highways where there is little traffic and hardly anyreflective radar targets.

Although in exceptional cases it may happen that actual blinding of theradar sensor has occurred in such situations and then the ACC systemwill fail to respond to the approach of a vehicle traveling in front ata lower speed, in practice this will not result in any impairment ofdriving safety because the ultimate responsibility for control of thevehicle still always lies with the driver, and the driver is compelledat any rate to keep his eye on the lane in front of his vehicle if forno other reason than to remain in the proper lane, so that obstacles infront of him would not escape his notice.

With available ACC systems, a display is provided on the dashboard ofthe vehicle, informing the driver either by lighting up or by a colorchange in a symbolic display of a vehicle traveling in front that arelevant target object has been selected (following mode). In addition,this display also informs the driver of the selected length of theinterval of time which determines the distance from the selected targetobject. Thus if the driver sees a vehicle emerge as traveling in frontand does not receive a message via the display that a relevant targetobject has been selected, the driver is able to recognize on the basisof this circumstance that the distance sensor is blind long before thedistance from the vehicle in front has declined to a critical level. Inthis way, the behavior of the system is transparent for the driver atall times.

The loss of convenience which results from an obstacle not beingdetected automatically in these rare cases is more acceptable for thedriver—in particular in sparsely populated regions having a dryclimate—than frequent system shutdowns because of presumed blinding ofthe sensor.

FIG. 3 shows a modified exemplary embodiment. After the system start(step S101), the system checks periodically in step S102 on whether thedriver has issued an activation command. Following an activationcommand, the ACC system is activated in step S103. A periodic blindnesscheck is then performed (step S104) during ongoing ACC operation,whether following or driving freely.

Only when a (presumed) blindness of the distance sensor has beendetected is a differentiation performed in step S105 to ascertainwhether the system is in following mode or in free driving mode. Infollowing mode, the routine branches off to step S106, where the ACCsystem is deactivated and a takeover instruction is issued to thedriver. As an example, FIG. 3 illustrates a variant in which the programis terminated (step S107) following this takeover instruction, so thedriver does not have an opportunity to reactivate the ACC system beforethe next system start. Here again, however, there may optionally also bea jump back to step S102 after step S106, thus permitting reactivationof the ACC system.

If the free driving mode has been detected in step S105, there may be animmediate jump back to step S104. As a result, this would mean that theblindness detection is being ignored in free driving mode. In theexample shown here, however, a few intermediate steps have been added inthis branch. In step S108 the driver receives the message “no objectsdetectable” via the dashboard display. However, the system is notdeactivated, so the cruise control function (regulation of speed at thedesired speed) remains available. The only purpose of the message is tonotify the driver as a precautionary measure that the distance sensormight be blinded, so that no vehicles traveling in front are detectable.

In step S109 a check is then performed periodically by ACC control unit14 to determine whether the distance sensor has again detected anobject. If this is the case, this means that in reality the sensor wasnot blinded but instead the presumed blindness detection is attributableonly to an absence of reflective objects. In this case the message (stepS108) is deleted in step S110 and the routine jumps back to step S104,continuing with normal cruise control.

FIG. 4 shows a modification of the method according to FIG. 3. StepsS202 to S206 correspond to steps S101 to S106 in FIG. 3. After detectingblindness in step S204 and detecting the “free driving” mode in stepS205, the driver here receives the message “no objects detectable,distance control off” in step S208. This indicates to the driver thatonly the cruise control set at the desired speed remains active, but thedistance control for following mode is not automatically resumed evenwhen new objects are detected. Instead, in step S209 a check is againperformed to determine whether the driver has entered a command for(complete) reactivation of the ACC system. Only following such a drivercommand is the message (step S208) deleted in step S210, with theroutine jumping back to step S203, where the activation command isexecuted. The system remains in the active mode if radar targets areagain detected in the meantime. Otherwise step S205 is run through againand there is either a switch to inactive mode (S206) or a switch topartially active mode (S208) in which the cruise control remains activebut the distance control is deactivated. Even in the inactive mode, thedriver is able to reactivate the ACC system via an activation command(checked in step S202).

FIG. 5 shows an embodiment in which the choice between the active andinactive mode of the ACC system is not based on a distinction betweenfree driving and following, but instead on the driver's behavior.

After system start in step S301, initialization is performed in stepS302 with a waiting time T being set at value T0 and a flag F being setat value 0. In step S303 the activation command is checked and in stepS304 the ACC system is activated if necessary.

With ongoing operation of the cruise control system, the blindness checkis performed in step S305, and if no blindness of the sensor is detectedwaiting time T and flag F (in the event they have changed in themeantime) are reset in step S306 to initial value T0 and 0,respectively, before repeating the blindness check in step S305.

If the blindness of distance sensor 12 is recognized in step S305, thena check is performed in step S307 to determine whether flag F has avalue of 1. Since this flag was initialized at 0, the result of thisquery will be negative in the first cycle. In step S308 a message isthen output to the driver, instructing the driver that the ACC systemwill be deactivated again because of presumed blindness of the distancesensor. Following that, flag F is set at value 1 in step S309. In stepS310, after waiting a certain time lag, a check is performed todetermine whether the driver has reentered the activation command withinthis time lag. If this is not the case, the ACC system is deactivated instep S311 and the routine jumps back to step S302, so the driver mayreactivate the system after reinitialization (in step S303).

However, if the driver enters the activation command within the time lagin step S310, he is thus giving notice that he considers the blindnessdetection to be incorrect and would like to resume the active state ofthe ACC system. The routine then jumps back to step S305 and theblindness check is repeated.

If there has been no change in ambient conditions in the meantime, theblindness of the sensor will be recognized again. However, the check instep S307 will now have a positive outcome because flag F has been setat 1 in step S309. In step S312, a timer is then started (if it is notalready running). A check is performed in step S113 to determine whetherwaiting time T, which initially had a value of T0 because of theinitialization, has elapsed since the start of the timer. In a waitingloop of length T, steps S304 and S307 are repeated. If an object isdetected again, the routine exits from the waiting loop at step S306.Otherwise, waiting time T is increased by a certain increment ΔT afterthe waiting time has elapsed in step S314 but only up to a maximum Tmax.The timer is reset. Steps S308, S309 and S310 are run through again.Step S309 remains ineffective, however, because flag F already has avalue of 1.

The renewed blindness detection in step S305 thus does not result inimmediate output of the message in step S308 in this cycle and insteadthis message is output only after waiting time T has elapsed. The systemthus remains active for the duration of waiting time T and onlythereafter, if the blinding of the sensor persists, is the driver againpresented with the choice in steps S308 through S310 as to whether hewants to allow the system to shut down because of presumed blindness orwhether he wants to continue to keep it active.

If the driver opts for the latter alternative, the routine again jumpsback to S305 and the waiting loop in step S306 is again run through butwith a longer waiting period of T+ΔT.

This cycle may be run through multiple times, waiting time T duringwhich the system remains active becoming longer by increment ΔT eachtime until reaching maximum value Tmax. In this way, the driver is ableto keep the system in the active mode with relatively rare interventionmeasures (renewed input of the activation command in step S310).

If it is ascertained at some time in step S305 that the distance sensoris no longer blind, then by resetting waiting time T and flag F in stepS306, the “memory” of the prior event is deleted and the system againbehaves as if it were in the initial state. Renewed detection ofblindness would then again result in immediate output of a message instep S308. Optionally, however, step S306 may also be omitted, so thatthe waiting times until the end of the trip are increased again and/orremain at the maximum value. In this case the driver will be burdenedless frequently by messages in step S308 if radar targets are detectedsporadically.

The embodiment shown in FIG. 5 requires occasional intervention on thepart of the driver in the form of entry of the activation command instep S310, but this command need be entered only at relatively longintervals due to the “learning ability” of the system, with theseintervals becoming longer and longer in the example presented here. Theadvantage of this embodiment is that the blindness detection is notignored completely even with an extended period of free driving in alow-reflection environment. The time lag built into step S310 has theadvantage that the driver does not become irritated due to immediatecessation of cruise control with the very first detection of blindnessor due to the associated implausible deceleration of the vehicle butinstead the driver is in a position to prevent such deceleration of thevehicle by promptly entering the reactivation command.

In the example shown here, waiting time T shows a linear increasecorresponding to constant increment ΔT, but embodiments in which thewaiting time increases progressively or according to any other curve arealso conceivable. The length of the waiting time may optionally alsodepend on how frequently radar targets have been detected in the past. Alow detection frequency indicates a low-reflection environment, so thewaiting time should be lengthened.

The embodiment according to FIG. 5 may also be combined with theembodiments described previously, so there is immediate deactivation ofthe ACC system in following mode, whereas the procedure according tosteps S307 through S314 is run through in free driving mode.

A detection check may of course also be performed according to step S2following the system start in the exemplary embodiments according to theFIGS. 3 through 5. It is also self-evident that the driver has theopportunity to deactivate the ACC system by a shutdown command at anytime. However, this is not shown in the flow charts for reasons ofsimplicity. Azimuth reflection.

1. A method for selecting an operating state of a cruise control systemfor a motor vehicle having a distance sensor and automatic blindnessdetection, the method comprising: checking, for automatic shutdown ofthe cruise control in the event of blindness of the distance sensor, atleast one additional condition; performing the shutdown only if the atleast one additional condition is met; and selecting, if no other one ofthe at least one condition is met when blindness of the distance sensoris detected, a partially active operating state in which the cruisecontrol remains active at a desired speed selected by the driver,wherein a distance control based on signals of the distance sensor isactivatable again only by a command by the driver.
 2. The method ofclaim 1, wherein at least one of the at least one additional conditionincludes the fact that a detection of the blindness of the distancesensor is immediately preceded by a “following” mode in which a vehicletraveling in front is selected as a target object and a distance fromthe target object is regulated.
 3. The method of claim 1, furthercomprising: outputting a message to the driver, when the blindness ofthe distance sensor is detected and no other one of the at least onecondition is met so that the cruise control is continued, to instructthe driver of a possible blindness of the distance sensor.
 4. The methodof claim 3, wherein the message includes a visual display and is deletedautomatically when the distance sensor detects new objects and theblindness detection system finds that there is no blindness of thedistance sensor.
 5. A method for selecting an operating state of acruise control system for a motor vehicle having a distance sensor andautomatic blindness detection, the method comprising: checking, forautomatic shutdown of the cruise control in the event of blindness ofthe distance sensor, at least one additional condition, wherein at leastone of the at least one additional condition is that when blindness isdetected, the blindness detection is the first blindness detection tooccur within a certain period of time; and performing the shutdown onlyif the at least one additional condition is met.
 6. The method of claim5, wherein if a current blindness detection is not the first time thatthe blindness has been detected, the cruise control is shut down onlyafter a certain waiting time has elapsed since the current blindnessdetection, during which time the blinding of the distance sensorpersists.
 7. The method of claim 6, wherein the waiting time is variableas a function of at least one of a frequency of reactivation commands bythe driver and a frequency of detection of target objects by thedistance sensor.
 8. The method of claim 5, wherein at least one of theat least one additional condition includes the fact that a detection ofthe blindness of the distance sensor is immediately preceded by a“following” mode in which a vehicle traveling in front is selected as atarget object and a distance from the target object is regulated.
 9. Themethod of claim 5, further comprising: outputting a message to thedriver, when the blindness of the distance sensor is detected and noother one of the at least one condition is met so that the cruisecontrol is continued, to instruct the driver of a possible blindness ofthe distance sensor.
 10. The method of claim 9, wherein the messageincludes a visual display and is deleted automatically when the distancesensor detects new objects and the blindness detection system finds thatthere is no blindness of the distance sensor.
 11. A cruise controlsystem for a motor vehicle, comprising: a distance sensor; a controlunit to regulate a speed of the vehicle as a function of a distance froma vehicle traveling in front, the distance being measured by thedistance sensor, or, if no vehicle traveling in front is detected, toregulate the speed to a desired speed selected by the driver, byperforming the following: checking, for automatic shutdown of the cruisecontrol in the event of blindness of the distance sensor, at least oneadditional condition, performing the shutdown only if the at least oneadditional condition is met, and selecting, if no other one of the atleast one condition is met when blindness of the distance sensor isdetected, a partially active operating state in which the cruise controlremains active at a desired speed selected by the driver, wherein adistance control based on signals of the distance sensor is activatableagain only by a command by the driver.
 12. A cruise control system for amotor vehicle, comprising: a distance sensor; a control unit to regulatea speed of the vehicle as a function of a distance from a vehicletraveling in front, the distance being measured by the distance sensor,or, if no vehicle traveling in front is detected, to regulate the speedto a desired speed selected by the driver, by performing the following:checking, for automatic shutdown of the cruise control in the event ofblindness of the distance sensor, at least one additional condition,wherein at least one of the at least one additional condition is thatwhen blindness is detected, the blindness detection is the firstblindness detection to occur within a certain period of time, andperforming the shutdown only if the at least one additional condition ismet.